•    1.3.2019

    Weather Forecast and Data Extraction Before Freeride Trip


Weather falls in the category of objective threats. We have no influence on it. Therefore, no matter where you’re planning to go, it’s necessary to check the forecast. What will the weather be on the day of skiing and what was the weather before that. Today's weather forecasts are quite reliable. It's good to check the following conditions: snowfall, wind, temperature, avalanche bulletin, terrain (inclination, orientation).


Snowfall

If there was any snowfall recently in the area where you plan to go, you already need to take extra caution.

Then what kind of snow was falling or in other words at what temperature the snow was falling. High temperatures for snowing, medium temperatures or low. It can also change during the snowfall. From warm to cold, which is perfect, or from cold to warm, which is the worst. Why? If it starts at high temperature and gradually descends, the wet snow at the bottom will provide a good grip with the surface and so will hold all the snow that fell above, in place. If it goes the other way around, start at low and gradually ascending, then we have a weak layer at the bottom which is perfect recipe for an avalanche.

Wind - the architect of avalanches

If wind was blowing during snowfall or after the snowfall, snow had to go somewhere. Usually it goes into couloirs, chutes and slipstream. It creates snow slabs, which can be highly unstable. Snow slabs can be small or enormous. It all depends on the weather. When you are on the wind affected area, you need to be extra careful, or even better, you turn around and go on a place that is safe.

Temperature

Temperature during snowing and in the first days after snowing effects on the transformation of the snow blanket. Snow transformation is faster at higher temperatures (around 0 °C). At lower temperatures the snow transformation is slower and the avalanche danger is decreasing slowly. Sudden rapid warming increases the likelihood of avalanches, ground avalanches, temperature fluctuations around 0 ° C stabilize the snow blanket.

Avalanche bulletin

The avalanche danger in Europe is evaluated on a five-point scale. Before going in the mountains, check the level on a local website. If you don’t know any, go on EAWS – European Avalanche Warning Services.

Terrain: Majority of avalanches are triggered between 20° and 50° angle. On the steeper slopes, the gravity does its job and the snow can't accumulate. The orientation of the slope is also important. Most avalanches that claimed fatalities were triggered by skiers and mountaineers on the NW, N and NE slopes. On this sites the snow is transforming slower (less sunshine). In spring, when the sun is already strong, S, SW and SE can be very dangerous because the sun speeds up melting and water increases the danger. 

Important questions you need to ask yourself before you go:

  • When was the last snowfall? And how much it fell.
  • What was the temperature when it was snowing?
  • From which direction the wind was blowing and at what speed.
  • What is the overall avalanche bulletin in this area?
  • What is the terrain aspect? Orientation, inclination.

*Additional: Snow test

With the cross-section of the snow cover, we get an insight into the structure and properties of individual parts of the snow cover, its profile and possibility to identify the so-called critical layers. These are parts where the snowy layers are poorly suppressed and are located in places where the hardness of the snow changes significantly. It is known that the avalanche is triggered precisely on these poorly adhered critical layers of snow cover. Indirectly, from the cross-section of the snow cover, we can also find the history of precipitation (snow, rain) in this area.

With testing we see how stable the snow cover is. We know many methods for testing: CT test, ETC test, Norwegian method and Swiss method.

The basics are more or less similar between the methods. If you want to know and learn the details, you have to go to an avalanche training. You can’t learn everything just by reading. You have to practice these things. They’ll explain and show you all the necessary details. And also give you some tips&tricks that can be very useful.

Overall, when you're checking the snow column, pay attention to different layers. How hard and thick these layers are. Optimal conditions are soft at the top and hard at the bottom. Gradual transition from soft to hard snow. Any hard layers in between, maybe even ice layer, can potentially be a dangerous weak layer, that will give up under load. Location of the test is also important. Make sure that the inclination an orientation is the same as the slope you plan to ski. Website that we found useful is LAWIS. It enables you to check the temperatures, wind, humidity and snow profile.

 


Writen by: Jan Palovsnik, freeride skier





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